Shock strut



Sept. 20, 1938. c. vv. JOHNSON SHOCK STRUT Filed June l2, 1,935

2 Sheets-Sheet 1 INVENToR. C10/9i V c//Y/VJ/Y BY MM ATTORNEYUNITEDSTATES PATENT OFFICE SHOCK STRUT Carl V. Johnson, South Bend,Ind., assigner to -Bendix Products Corporation,

South Bend,

Ind;, a corporation of Indiana Application June 12, 1935, Serial No.26,148

This invention relates to shock absorbing struts 2 Claims` designedparticularly for use with aircraft. but also adapted for use in otherdevices where it is desired to absorb impact loads.

In the smaller types of aircraft, ithas been found impractical to employshock absorbers ofv a conventional form, because of the complexity ofthe absorbing device, the increased weight, and the added cost of thestructure. It hasbeen common practice, therefore, to build such aircraftwith rigid struts, depending on the resiliency of pneumatic tires toabsorb the shocks of landing and taxying the craft on the ground. As arei sult ,of this, aircraft has been subjected to severe shocks andstrains which resulted in damage to the craft and impaired the comfortof the occupants thereof.

An object of this invention is therefore toprovide a simple shockabsorber capable of absorbing high shock per unit weight of the strut.

A further object of the invention is to provide means for trapping agiven quantity of air in a strut to move the strut to thefully expandedposition when not subjected to load.

Another object of the invention is to provide a strut wherein a pressureis constantly exerted upon the strut sufficient to keep it fullyexpanded during maneuvers in the air.

Another object of the invention is to provide a shock absorbing strutwherein the shock is absorbed by exerting pressure on a uid and forcingit through an orifice.

ergy absorbing capacity is small.

Other objects and advantages of this invention will be apparent fromthefollowing detailed description, together with the accompanyingdrawings, submitted for purposes of illustration only and notintended todefine the scope of the invention, reference being had for that purposeto the subjoined claims.

. In the drawings, wherein similar yreference characters refer tosimilar parts throughout the several views:

FigureA 1 is a sectional'4 view of a shock strut embodying the presentinvention;

Figure 2 is a view taken on the lin ure 1;

e 2 2 of Figcylinder I2 is provided with a fitting I6 adapted isthreaded to receive a retaining nut 24 which o holds a washer 26 ofrubber or other suitable resilient material. The washer 2B engages theinner surface of the cylinder I2 to form a fluid tight contact betweenthe cylinders I0 and I2.

The retaining nut 24 is lockedin place by a lock 'A ing nut 28 having acontracted outer section 30 designed to prevent a gravity actuatedpressure responsive washer valve 32 from escaping. The valve 32 is soproportioned that when moved to the upper position it will close theauxiliary orices 22. The fitting I6, closing the lower end of thecylinder I2, is provided with a projection 34 adapted to slide throughthe contracted section '30 of the locking nut 28 to urge the washervalve 32 into engagement with the plunger I8 carried by the innercylinder 'Ito limit the downward movement of the inner cylinder I0. f

A sleeve 36, interposed between the inner and outer cylinders i0 and I2,limits the upward movement'of inner cylinder I0. The sleeve 36 engages aprojection 38 carried by the plunger I8 at the lower end, and aninwardly disposed projection 40 carried by a locking sleeve 42 screwedonto the upper end of the outer cylinder I2.

It will be understood that the connection between the upper and lowerends of the cylinder I0, the fitting I4 and the plunger I8 respectively,as well as the connection between the lower end of the cylinder I2 andthe fitting IB may be a welded, shrunk, press fit, threaded connectionor the parts may be secured together in fluid tight relation in" anyother desired manner.

The assembly of this device is as follows. yA quantity of liquid such asoil of suitable viscosity is placed in the outer cylinder I2.v The innercylinder Ill,y having the plunger I8 xed thereto, is then inserted intothe upper end of the cylinder l2. The washer 26 engages the inner wallsof the cylinder I2 in fluid tight relation, and prevents the escape ofair and liquid. The sleeve 36 is then placed on the inner cylinder I@and the cylinder forced downwardly, whereupon the liquid is' compressedand forced to tlowthrough the central orice 2|! of the plunger I8, intothe inner cylinder I to compressv the air contained therein. Thethreaded locking sleeve d2 is then tightened on the cylinder i2. Theprojection i engages the Nupper end of the sleeve 36 to prevent thecylinders Ill and I2 from becoming disassembled.

In operation when a shock is encountered, the

cylinder IB tends to telescope Within the cylinder I2. The telescopingaction is resisted by the liquid contained in the cylinder I2.. Apressure is therefore exerted on the liquid which forces the washervalve 32 upwardly to close the auxiliary orices 22 in the plunger i8.The liquid in the cylinder I2 then flows through the central orifice2li-into the upper cylinder l@ to absorb the shock.

As the liquid is transferred into the cylinder l@ from the cylinder l2,the air in the cylinder l@ is compressed. When the load is removed fromthe strut, the liquid pressure in the cylinders I and l2 becomesequal/ized, whereupon the valve 32 uncovers the auxiliary orifices 22,and the force of the compressed air in the cylinder i@ forces the liquidthrough both the central and the auxiliary orifices 2 and 22respectively.

It thus appears that when the strut is subjected to shock or staticloadthe iiuid iiows from the cylinder I2 into the cylinder I0 through asingle orice, and when the load is removed the iuid is forced by thepressure of the trapped air from the cylinder IIJ into the cylinder I2through a plurality of orifices. A quick return action is thus obtained,and sumcient air pressure, is main.

tained in the cylinder I0 to hold the strut `in the fully extendedposition at all times when not subjected to load. It will be understoodthatA any desired pressure may be maintained above the oil by merelyvarying the dimensions of the respective parts of thev strut, orby'placing the oil in the upper cylinder I0 before the strut isassembled. If desired, a quantity of oil may be placed in both of thecylinders I0 and I2 to vary the pressure of the trapped air when thestrut is assembled. f

Figure 3 inustrates a modified form of the 1n-l vention wherein theplunger II8, fixed to the cylinder IIU, is provided with a threaded plugII 9 having a central oriiice |20. The washer |28 engages the innerwallsof the outer cylinder I|2 and is vresiliently held in place between theplunger IIB and the plug I9 by means 'of Belville washers I2 I.

The telescoping movement nof the inner cylinder IIU within the outercylinder |.I2 is limited,

in the downward direction, when the plug I I9 engages the projection |34carried by the iittingA i le. The Belville washers I2l resilientlyabsorbthe shock ofl impact when 'the respective parts engage each other. Theupward movement of the inner cylinder III] with respect to the outercyl-4 carried by the projection M0,

In the embodiment of the invention illustrated in Figure 4, the washer226 is held between the plunger 2id, fixed in the lower end of the innercylinder 2id, and a threaded plug 225 engaging the plunger 2 It.

The' operation of this device is similar in many respects to theoperation of the other embodiments. When the strut is subjected to load,the inner cylinder 2 It! moves downwardly within the outer cylinder 2I2,thereby exerting pressure on the oil in the cylinder 262 and forcing itthrough the central orifice 22d in the plunger 2I8. lThe air above theoil level in the inner cylinder 2i@ is thereby compressed, as the oilflows into the cylinder 2id. When the load is removed, the pressure ofthe trapped air forces the oil from the cylinder 2id, through theorifice 220 into the cylinder 222 to expand the strut, preparatory tothe next cycle of operation.

W'hile the invention has been described with particular reference tocertain preferred embodi-` ments, it is not intended to limit the scopeof the invention to the embodimentsdescribed and illustrated, norotherwise than by the terms of the following claims.

I claim: e

1. A shock strut comprising telescoping inner and outer cylinders, iiuidand liquid in the cylin- `ders', a partial closure comprising a plungerhaying a plurality of aperturesand an apertured member Kassociatedtherewith for one end of the inner cylinder, pressure operated meansinterposed between the plunger and the apertured member to vary the rateof'iiow between the inner land outer cylinders dependent on whether thestrut is being compressed or expanded.

2. In a shock strut a pair of telescoping cylinders, liquid and iiuid inthe cylinders, a head comprlsing a plurality of parts for one end of oneof the cylinderskpacking means engaged between two adjacent parts of thehead and adapted to engage the walls of the outer cylinder, main andauxiliary orifices in one of the' head parts, and a gravity actuatedvalve supported by another of the head' parts and adapted-to close theauxiliary orifices under certain operatingconditions.

CARL v. JOHNSON.

